Some properties of a hexadecane hydroxylation system in rabbit intestinal mucosa microsomes

Among many different tissues of rabbit, hexadecane hydroxylation activity was found in only small intestine and liver microsomes. Both activities for hexadecane and decane hydroxylation in intestinal microsomes were significantly higher than those in liver microsomes. In contrast, the hydroxylation activities of p-xylene, benzo(a)pyrene, and decanol, and the demethylation activity of aminopyrine in the former were much lower than those in the latter. The intestinal microsomes converted [1-14C]hexadecane to cetyl alcohol, but not further to palmitic acid. Hexadecane hydroxylation activity was found to be markedly stimulated by non-ionic detergents such as Triton X-100, Nonident P-40, and Emulgen 913. Phosphatidylcholine and phosphatidylethanolamine stimulated the activity to a lesser extent. The hydroxylation was inhibited by various aliphatic hydrocarbons with carbon numbers larger than 10, but not by aromatic and polycyclic hydrocarbons. Hexadecane hydroxylation activity was solubilized from the intestinal microsomes and reconstituted with a partially purified cytochrome P-450 fraction, and intestinal NADPH-cytochrome c reductase, or spinach ferredoxin and ferredoxin-NADP reductase. The chromatography of the crude cytochrome P-450 preparation on hydroxylapatite separated at least two cytochrome P-450 fractions; one preferentially hydroxylating hexadecane, and the other preferentially hydroxylating myristic acid. The results suggest that rabbit intestinal mucosa microsomes had a cytochrome P-450 species specialized for hexadecane hydroxylation.